Interest in and demand for wireless multimedia applications are growing rapidly. Multicast over wireless networks enables efficient distribution of data including but not limited to multimedia data and entertainment programs (video, audio, file and text) to many receivers simultaneously. However, multimedia data delivery requires high reliability and bandwidth efficiency. Wireless links are unreliable with time-varying and burst link errors. Especially in multicast applications, different receivers of the same program may experience heterogeneous channel conditions and receivers may leave or join during the session so that the topology of receivers changes. There is no link layer retransmission and no link layer adaptation for multicast in many wireless networks, for example, current IEEE 802.11 networks. A wireless device may be handed off from one access point (AP)/base station (BS) to another. As used herein, “/” denotes alternative names for the same or similar components or structures. That is, a “/” can be taken as meaning “or” as used herein. A wireless device includes laptops, dual mode smart phones, personal digital assistants (PDAs), end devices, clients, client devices, mobile devices mobile terminals, multicast clients, multicast client devices, receivers etc. Data frame transmission is interrupted and a number of data packets are lost to the receiver during periods of handoff. Furthermore, multiple wireless APs/BSs are connected to a multicast server/source via a high speed wired network. The channel conditions of the clients in one cell may be dramatically different from the channel conditions of clients in another cell.
A unicast communication is a one-to-one communication between two entities. A broadcast communication is a communication between one and all other entities in the communication system. A multicast communication is a one-to-many communication between an entity and a plurality of other entities in the communication system, where the plurality of other entities may include all other entities in the communications system. In many wireless multicast systems, the forward error correction codes (FEC) are used within a packet at the physical layer to protect against multi-path fading and interference and to reduce the packet errors. To recover the lost packets in wireless networks, the FEC codes are also applied across packets at the transport and application layers. However, the wireless channel conditions are time-varying and the multiple clients in multicast networks experience heterogeneous channel conditions. The FEC codes are normally used according to the worst channel conditions to ensure the receiving quality of all the receivers in the desired service area. This results in a large overhead and requires a great deal of radio resources for retransmission. Another technique to improve reliability is to use retransmission of lost packets, also called Automatic Repeat reQuest (ARQ). In a multicast scenario, ARQ is not very efficient. For example, if client A loses packet 1 and client B loses packet 2. The source/server retransmits both packet 1 and packet 2.
In some reported multicast systems, a hybrid ARQ scheme is described, which combines ARQ and FEC and is more efficient than pure ARQ. The retransmitted packets in hybrid ARQ are the parity packets generated by a FEC code, which can be used to correct different lost information packets by different receivers. For example, client A loses packet 1 and client B loses packet 2 and if a Reed-Solomon FEC code is used to generate the parity packets with cross-packet erasure coding, the source/server only needs to retransmit/multicast one FEC parity packet. Client 1 can use the retransmitted FEC parity packet to recover packet 1 and Client B can use the same FEC parity packet to recover packet 2.
However, in the previous multicast ARQ or hybrid ARQ schemes, the retransmitted packets are sent in a single multicast group, either the same multicast group as the source data packets or a separate multicast group. Multiple receivers may experience time-varying and heterogeneous channel conditions. If one receiver in a particular cell requests a lot of retransmitted packets, these retransmitted packets will be sent multicast in all the wireless cells even though the receivers in other cells do not need so many retransmitted packets. This method, thus, wastes the radio bandwidth of the other cells.
Scalability in terms of the number of APs/BSs and the number of clients is an important issue to resolve. It would be advantageous to have a reliable and scalable wireless multicast system and that efficiently utilizes the wireless bandwidth.